ABSTRACT
The ability to manipulate and interact with particles at small (micro and nano) scales has been essential to many recent advances in science and technology. Several techniques such as mechanical manipulators,1-3 electrophoresis,4,5 dielectrophoresis6 (DEP), electroosmosis,7,8 microŒuidics,9-11 and magnetic12-14 manipulation have been created in the past few decades to address this challenge. Optical manipulation of particles offers an attractive choice due to its inherent Œexible and noninvasive nature. In the „eld of optical manipulation, only two technologies have emerged as most inŒuential. The „rst technique, optical tweezers (OTs), which was invented by Ashkin et al.,15 traps particles through the optical gradient forces16-19 resulting from a tightly focused laser source. OT is capable of trapping micro-and nanoscale particles in three dimensions and has been a critical tool in studying detailed biological and chemical mechanisms. However, to stably trap the particles of interest, OT requires very high optical power intensities, which limits its effectiveness in performing high-throughput and large-scale optical manipulation functions and it can potentially damage the trapped objects,16,20,21 especially biological materials. The second optical manipulation technique, called optoelectronic tweezers22 (OET), works based on the principle of light-induced dielectrophoresis (LIDEP) force. In this technique, the optical „eld is not used directly to manipulate the particles; instead, it interacts with a photoconductive material to create virtual electrodes which will form electric „eld gradient landscapes that will trap the particles based on the DEP principle. Therefore, OET requires optical power intensities approximately 5 orders of magnitude smaller than OT and is capable of massively parallel manipulation of particles over larger areas. As a result, it is possible to achieve large-scale and high-throughput optical manipulation of particles using OET.
